java集合类专题

 

package com.alibaba.caseutils.test;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class testmap {
    public static void main(String[] args) {
        Map<String,String> heads = new HashMap<String, String> ();
        heads.put ( "a","第一个" );
        heads.put ( "a","第一个" );
        heads.put ( "b","第二个" );
        heads.put ( "c","第三个" );
        if(heads!=null){
            System.out.println (heads.entrySet ());
　　　　　　　　#[a=第一个, b=第二个, c=第三个]
            System.out.println ();
            for(Map.Entry<String,String> head: heads.entrySet ()){
                System.out.println (head);
                System.out.println (head.getKey ());
                System.out.println (head.getValue ());
            }
        }

    }


}

 第二种方式，思路把map集合利用map.entryset  转化成set集合，在利用set集合的 迭代器进行遍历

package com.alibaba.autotest_v2;

import javax.swing.text.InternationalFormatter;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class Cmap {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("aa", 123);
        map.put("aa", 123);
        map.put("bb", 456);
        //遍历
        Set<Map.Entry<String,Integer>> set = map.entrySet();
        Iterator<Map.Entry<String,Integer>> iterator = set.iterator();
        while (iterator.hasNext()){
           Map.Entry<String, Integer> keys =iterator.next();
            System.out.println("key+"+keys.getKey()+";value="+keys.getValue());
        }
    }
}

key+aa;value=123
key+bb;value=456

Process finished with exit code 0

 

package com.alibaba.autotest_v2;

import javax.swing.text.InternationalFormatter;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class Cmap {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("aa", 123);
        map.put("aa", 123);
        map.put("bb", 456);
        Set<Map.Entry<String,Integer>> set=map.entrySet();
        for(Map.Entry<String, Integer> ME:set){
            System.out.println(ME.getKey());
            System.out.println(ME.getValue());
        }
       }
}

 集合类图常用总览

1.list与set 本质的区别是list存储元素list可以重复，set则不行

 

 

 

 

 

 

 

 

 

package com.alibaba.caseutils.test;

import java.sql.Array;
import java.util.*;

public class testmap {
    public static void main(String[] args) {
        Set<String> set= new HashSet<String> ();
        set.add ( "褚志强" );
        set.add ( "阿强" );
        set.add ( "褚志强" );
        set.add ( "安命" );

        Iterator<String> iterator=set.iterator ();
        while (iterator.hasNext ()){
            String ele=iterator.next ();
            System.out.println (ele
            );
        }
    }
}

褚志强
阿强
安命